This invention relates to wallboards and particularly to a wallboard comprising a low-strength core and having a decorative plastic facing. The invention is particularly concerned with wallboards of the type suitable for use aboard ship or in the construction of hospitals, nursing homes, schools, office buildings, motels, homes and similar structures. The decorative plastic facing is particularly desirable, in these and in other applications, because of its availability in a large variety of patterns and also because of the ease with which it can be cleaned.
Currently, most decorative ship's bulkheads consist of a low-strength core composition of asbestos fiber, diatomaceous silica and organic binder, the core being provided on both sides with a laminated facing consisting of sheets of resin-impregnated paper covered by a decorative sheet and finally a transparent sheet impregnated with a synthetic resin. The resin is typically of melamine-formaldehyde. Melamine-formaldehyde is especially suited as a facing material because of its resistance to damage and also because of its transparency.
For similar, land-based installations, other plastic facing materials in use include the following in the form of thermoplastic or thermoset sheets: acrylic-polyvinyl chloride, phenylene oxide based thermoplastic sheets, polycarbonates, methacrylates, and glass fiber reinforced polyesters.
The faced asbestos wallboard is highly decorative, fire resistant, light in weight, and durable. However, it is expensive and, because of the presence of asbestos fibers, is hazardous to work with.
The synthetic resin-containing facings generally have high hygrometric coefficients so that they tend to shrink when exposed to conditions of low humidity. Shrinkage of the facing can cause the low-strength core to split so that the facings and part of the core tend to curl outwardly. In the case of faced asbestos cores, shrinkage of the facing is not considered serious because the internal bond strength of the core is usually sufficient to resist splitting except under conditions of extremely low humidity. Some difficulty has been experienced, however, where the faced asbestos core wallboard is exposed to hot, dry air.
Alternative low-strength wallboard materials are usable in various applications, but are not generally faced with melamine-formaldehyde or other shrinkable resin-containing facings because they have somewhat less internal bond strength than the aforementioned asbestos core and are subject to splitting even under commonly encountered conditions of low humidity. The most common low-strength core is gypsum, which is usually supplied with paper facing. Gypsum typically has an internal bond strength somewhat lower than that of the typical asbestos core of comparable size. This difference is such that typical faced gypsum cores exhibit a tendency to split at humidity levels below about thirty percent, while asbestos composition cores with similar facings are reasonably resistant to splitting at somewhat lower humidity levels.
While asbestos compositions and gypsum are the most commonly used low-strength core materials, various other non-metallic, non-combustible materials are usable as low-strength core materials and may be used in wallboards so long as they are provided in sufficient density, and with any necessary reinforcement, to make them suitable as structural materials. These include, for example, ceramic fiberboard, reinforced expanded perlite and hydrous calcium silicate.
The general object of this invention is to provide a faced wallboard having a low-strength core which is stable under conditions of low humidity. In accordance with the invention, a wallboard comprising a low-strength core is provided with facings on both sides, each facing comprising a synthetic resin-containing sheet having a tendency to shrink under conditions of low humidity and a sheet of metal foil, preferably steel, located between the core and the facing.
Another object of the invention is to improve the resistance of faced asbestos composition wallboard to splitting under conditions of extremely low humidity.
Another object of the invention is to enable wallboard core materials such as gypsum to be faced with melamine laminates and other synthetic resin-containing materials which tend to shrink under conditions of low humidity.
Still further objects of the invention include the provision of an inexpensive wallboard having adequate fire resistance, and structural integrity; and the provision of a wallboard particularly suited for a ship's bulkhead. The accomplishment of these objects and other objects of the invention will appear in the following detailed description when read in conjunction with the drawings.